1. Technical Field of the Invention
The present invention relates to the field of integrated circuit, and more particularly to configurable gate array.
2. Prior Art
A configurable gate array is a semi-custom integrated circuit designed to be configured by a customer after manufacturing. It includes field programmable gate array (FPGA) and mask-programmed gate array (MPGA). U.S. Pat. No. 4,870,302 issued to Freeman on Sep. 26, 1989 (hereinafter referred to as Freeman) discloses a configurable gate array—FPGA. It contains an array of configurable logic elements (also known as configurable logic blocks) and a hierarchy of configurable interconnects (also known as programmable interconnects) that allow the configurable logic elements to be wired together. Each configurable logic element in the array is in itself capable of realizing any one of a plurality of logic functions (e.g. shift, logic NOT, logic AND, logic OR, logic NOR, logic NAND, logic XOR, arithmetic addition “+”, arithmetic subtraction “−”, etc.) depending upon a first configuration signal. Each configurable interconnect can selectively couple or de-couple interconnect lines depending upon a second configuration signal.
Math functions are widely used in various applications. To meet the speed requirements, many high-performance applications require that these math functions be implemented in hardware. In conventional configurable gate arrays, math functions are implemented in fixed computing elements, which are part of hard blocks and not configurable, i.e. the circuits implementing these math functions are fixedly connected and are not subject to change by programming. Apparently, fixed computing elements would limit further applications of the configurable gate array. To overcome this difficulty, the present invention expands the original concept of the configurable gate array by making the fixed computing elements configurable. In other words, besides configurable logic elements, the configurable gate array comprises configurable computing elements, which can realize any one of a plurality of math functions.